The results of treatment of idiopathic thrombocytopenic purpura (ITP) were analysed in a series of 41 patients 2 to 10 years (median 4 years) after initial treatment. There was one spontaneous remission. A good or fair long-term result was obtained in 11 patients after prednisone treatment, in 20 of 24 patients after splenectomy, and in 3 of 4 patients after immunosuppressive treatment. Short duration of symptoms and rapid response to prednisone had some value in predicting a good long-term result of prednisone treatment. Young age, a good response to prednisone and splenic sequestration of platelets were associated with good results after splenectomy, as was rapid postoperative normalization of platelet counts. These factors were unable to disclose with certainty a refractoriness to splenectomy. Nevertheless splenectomy was regarded to be the treatment of choice in all patients not adequately controlled with corticosteroids.